FIG. 1 of the accompanying drawings schematically illustrates a conventional butterfly valve arrangement 10 in which a butterfly plate 12 positioned in a duct 14 is rotated about an axis 15 defined by a spindle or shaft 16 in order to vary the rate at which fluid (indicated by the arrow 72) flows through the duct. Typically, the plate 12 is rotated via torque applied by an external actuator 20 through the shaft 16.
A series of arrows 22 generally illustrates the static pressure profile resulting from the hydrodynamic forces acting on the butterfly plate 12. The overall effect of the static pressure may be represented by a center of pressure (indicated by the dashed arrow 24) which tends to force the plate 12 to the closed position. This force must be countered or overcome by energy supplied to the actuator 20 in order to retain the position of the plate 12 or further open the valve 10.
As a general matter, in order to lower the energy required to match or exceed the hydrodynamic forces acting on the plate 12, the center of pressure 24 should be favorably altered in relation to the axis 15 of rotation. That is, either the center of pressure 24 should be aligned with or moved closer to the shaft 16, or the shaft should be aligned with or moved closer to the center of pressure.
Prior approaches to designing butterfly valves appear to have embodied the various assumptions described below, each of which is rejected for particular embodiments of the present invention, and all of which are rejected for preferred embodiments thereof.
A first of these assumptions, applicable to butterfly valves with internally-disposed actuators, is that the actuator 20 should be secured to the duct 14 with its output arm secured to the plate 12, thereby operating in a push-pull mode to control the position of the plate (see, e.g., U.S. Pat. No. 3,794,288). Positioning the actuator in that manner limits practicable design options and can result in unnecessarily high flow obstruction by the actuator. Accordingly, the present invention rejects this first assumption for all embodiments thereof, and provides heretofore unrecognized advantages in the design and operation of butterfly valves.
A second of the assumptions is that the hydrodynamic forces acting on the plate 12 must be overcome through brute force applied by torquing the shaft 16, or by pushing on the plate. A partial exception thereto is the invention disclosed in U.S. Pat. No. 3,971,414 Illing. Illing provides a butterfly valve in which a servo-tab portion of the plate 12 is angled relative to the remainder as needed to compensate for excessive hydrodynamic forces otherwise acting on the plate at various rotational positions. The servo-tab portion is angled in response to torque which is applied to the shaft 16 and transferred to the servo-tab via a combination of mechanical linkage elements secured to the shaft and the plate 12. The present invention rejects this assumption and differs substantially from the Illing invention for reasons which will become evident from the following text.
A third of the assumptions is that the relative motion between the plate 12 and the shaft or spindle 16 is one of simple rotation. This assumption is understandable in view of the fact that in order to close the valve 10, the diameter of the plate 12 must be substantially the same as the inside diameter of the duct 14 unless a stepped duct is provided. However, acceptance of this assumption eliminates from consideration a number of advantageous design options. As is further explained by the following description, which includes the appended claims and accompanying drawings, the present invention rejects this assumption for preferred embodiments thereof. In these embodiments, the plate is secured to the pivot shaft in such manner that it is both revolvable and translatable relative to the shaft. This arrangement provides the ability to achieve closer alignment of the center of pressure 24 with the shaft when the valve is open, thus reducing the externally-supplied energy required to maintain a given flow rate, and further provides for far more use of hydrodynamic force in adjusting flow rates. This in turn should provide the ability to use smaller actuators, thereby lowering the overall weight of the butterfly valve structure.
An objective of the invention is to provide smaller and lighter butterfly valves.
Another objective is to provide butterfly valves having less sensitivity to vibration.
A further objective is to reduce the energy that is required to operate butterfly valves.
A still further objective is to provide butterfly valves with internally-disposed actuators which are positioned to minimize obstruction to flow.